U.S. patent number 8,581,209 [Application Number 12/362,323] was granted by the patent office on 2013-11-12 for fluorescent monitoring of microcapsule oxidation.
This patent grant is currently assigned to Southwest Research Institute. The grantee listed for this patent is Jenny J. Finkbiner, Nitin Nitin, James D Oxley. Invention is credited to Jenny J. Finkbiner, Nitin Nitin, James D Oxley.
United States Patent |
8,581,209 |
Oxley , et al. |
November 12, 2013 |
Fluorescent monitoring of microcapsule oxidation
Abstract
The present disclosure relates to microcapsules that include a
shell material and a core material. The core material of the
microcapsules contains an environmentally sensitive luminescent
colorant which exhibits characteristics of an emitted wavelength
bandwidth, a peak intensity for emission and a time for
luminescence decay, one or more of the characteristics capable of
changing upon exposure to a given environment, and a luminescent
standard which exhibits characteristics of an emitted wavelength
bandwidth, a peak intensity for emission and a time for
luminescence decay, one or more of the characteristics do not
change upon exposure to said given environment.
Inventors: |
Oxley; James D (San Antonio,
TX), Finkbiner; Jenny J. (Helotes, TX), Nitin; Nitin
(Helotes, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Oxley; James D
Finkbiner; Jenny J.
Nitin; Nitin |
San Antonio
Helotes
Helotes |
TX
TX
TX |
US
US
US |
|
|
Assignee: |
Southwest Research Institute
(San Antonio, TX)
|
Family
ID: |
42353412 |
Appl.
No.: |
12/362,323 |
Filed: |
January 29, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100187439 A1 |
Jul 29, 2010 |
|
Current U.S.
Class: |
250/459.1;
428/403; 428/402.2; 250/200; 427/163.2; 427/331 |
Current CPC
Class: |
G01N
21/278 (20130101); C09K 11/06 (20130101); B01J
13/10 (20130101); C09K 11/025 (20130101); C09B
67/0097 (20130101); G01N 21/6408 (20130101); B01J
13/14 (20130101); Y10T 428/2991 (20150115); Y10T
428/2984 (20150115); G01N 2021/7786 (20130101) |
Current International
Class: |
G01N
21/64 (20060101); B05D 3/00 (20060101) |
Field of
Search: |
;250/459.1,200
;428/3,220,339,402 ;427/331,163.2,2.13 ;422/82.07,82.05,82.09 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Guice et al. (Proceedings of the Second Joint EMBS/BMES Conference,
2002, p. 1712-1713). cited by examiner .
McNamara, et al., "Optochemical Glucose Sensing in Volume Limited
Samples," available at
http://www.ieee.org/organizations/pubs/newsletters/leos/apr98/optochemica-
l.htm, retrieved on Mar. 23, 2009. cited by applicant.
|
Primary Examiner: Seidleck; James J
Assistant Examiner: Pourbohloul; S. Camilla
Attorney, Agent or Firm: Grossman, Tucker et al
Claims
What is claimed is:
1. Microcapsules comprising a shell material; a core material,
wherein said core material includes: i) an environmentally
sensitive luminescent colorant present in the range of 1 ppm to 50
ppm which exhibits characteristics of an emitted wavelength
bandwidth, a peak intensity for emission and a time for
luminescence decay, one or more of said characteristics capable of
changing upon exposure to a given environment; ii) a luminescent
standard present in the range of 1 ppm to 50 ppm which exhibits
characteristics of an emitted wavelength bandwidth, a peak
intensity for emission and a time for luminescence decay, one or
more of said characteristics do not change upon exposure to said
given environment and wherein said luminescent standard is selected
from one or more of the following: sulfonated coumarin dyes,
sulfonated rhodamine dyes, sulfonated xanthene dye, sulfonated
cyanine dyes, and quantum dots; and iii) an ingredient, wherein
said ingredient includes one or more of the following:
pharmaceuticals, flavorants, or attractants and wherein said
environmentally sensitive luminescent colorant has a first rate of
oxidation correlated with a second rate of oxidation of said
ingredient; and iv) a hydrocarbon solvent; and one or more layers
formed on the microcapsule surface selected from the group
consisting of polyanions, polycations and combinations thereof,
wherein said environmentally sensitive luminescent colorant and
said luminescent standard are measurable through said shell without
rupturing said microcapsules.
2. The microcapsules of claim 1, wherein said emitted wavelength
bandwidth of said environmentally sensitive luminescent colorant is
capable of changing or shifting in the range of +/-50 nm.
3. The microcapsules of claim 1, wherein said peak intensity for
emission of said environmentally sensitive luminescent colorant is
capable of shifting in the range of +/-50 nm.
4. The microcapsules of claim 1, wherein said time for decay of
said environmentally sensitive luminescent colorant is capable of
changing within +/-5 seconds.
5. The microcapsules of claim 1, wherein said environmentally
sensitive luminescent colorant exhibits a first excitation
wavelength .lamda..sub.exc and said luminescent standard exhibits a
second excitation wavelength .lamda..sub.exs, and said
environmentally sensitive luminescent colorant exhibits a first
emission wavelength .lamda..sub.emc and said luminescent standard
exhibits a second wavelength .lamda..sub.ems which are
different.
6. The microcapsules of claim 1, wherein said environmentally
sensitive luminescent colorant and said luminescent standard
exhibit a Hildebrand solubility values (.delta.) that are within
+/-2.0 units of one another, as measured in (MPa).sup.1/2.
7. A method of forming microcapsules, comprising: mixing a
hydrocarbon solvent, an environmentally sensitive luminescent
colorant, a luminescent standard, and an ingredient wherein said
ingredient includes one or more of the following: pharmaceuticals,
flavorants, or attractants to form a core material, wherein said
environmentally sensitive luminescent colorant exhibits
characteristics of i) an emitted wavelength bandwidth, ii) a peak
intensity for emission and iii) a time for luminescence decay, one
or more of said characteristics capable of changing upon exposure
to a given environment and wherein said environmentally sensitive
luminescent colorant has a first rate of oxidation correlated with
a second rate of oxidation of said ingredient and said luminescent
standard exhibits characteristics of i) an emitted wavelength
bandwidth, ii) a peak intensity for emission and iii) a time for
luminescence decay, one or more of said characteristics do not
change upon exposure to said given environment and said luminescent
standard is selected from one or more of the following: sulfonated
coumarin dyes, sulfonated rhodamine dyes, sulfonated xanthene dye,
sulfonated cyanine dyes, and quantum dots; and encapsulating said
core material in a shell material forming microcapsules by complex
coacervation; and forming one or more layers on the microcapsule
surface selected from the group consisting of polyanions,
polycations and combinations thereof using layer by layer
formation, wherein said environmentally sensitive luminescent
colorant is present in the range of 1 ppm to 50 ppm and said
luminescent is present in the range of 1 ppm to 50 ppm and said
environmentally sensitive luminescent colorant and said luminescent
standard are measurable through said shell without rupturing said
microcapsules.
8. The method of claim 7, wherein said emitted wavelength bandwidth
of said environmentally sensitive luminescent colorant is capable
of changing or shifting in the range of +/-50 nm.
9. The method of claim 7, wherein said peak intensity for emission
of said environmentally sensitive luminescent colorant is capable
of shifting in the range of +/-50 nm.
10. The method of claim 7, wherein said time for decay of said
environmentally sensitive luminescent colorant is capable of
changing within +/-5 seconds.
11. The method of claim 7, wherein said environmentally sensitive
luminescent colorant exhibits a first excitation wavelength
.lamda..sub.exc and said luminescent standard exhibits a second
excitation wavelength .lamda..sub.exs, and said environmentally
sensitive luminescent colorant exhibits a first emission wavelength
.lamda..sub.emc and said luminescent standard exhibits a second
wavelength .lamda..sub.ems which are different.
12. The method of claim 7, further comprising cross-linking said
shell material.
13. The method of claim 7, further comprising soaking said
microcapsules in clay.
14. The method of claim 1, wherein said luminescent standard and
said luminescent colorant have Hildebrand solubility parameter
values (.delta.) that are within +/-2.0 units of one another, as
measured in (MPa).sup.1/2.
15. A method of identifying changes in a core material in a
microcapsule due according to claim 1, to environmental exposure
comprising: (i) providing microcapsules including a core material
whose environmental sensitivity is to be monitored, said
microcapsule containing an environmentally sensitive luminescent
colorant exhibiting a first set of luminescent characteristics and
an environmentally insensitive luminescent standard exhibiting a
second set of luminescent characteristics; (ii) measuring the first
and second set of luminescent characteristics of the microcapsules
at a time t.sub.0 and t.sub.1 in a given environment; (iii)
examining the difference between the first and second sets of
luminescent characteristics of said environmentally sensitive
luminescent colorant and said luminescent standard; (iv)
identifying a change in said core material associated with the
difference in luminescent characteristics identified in step
(iii).
16. The method of claim 15, wherein said environmentally sensitive
luminescent colorant exhibits characteristics of an emitted
wavelength bandwidth, a peak intensity for emission and a time for
luminescence decay, one or more of said characteristics capable of
changing upon exposure to a given environment and said luminescent
standard exhibits characteristics of an emitted wavelength
bandwidth, a peak intensity for emission and a time for
luminescence decay, one or more of said characteristics not
changing upon exposure to said given environment.
17. The method of claim 15, wherein said environmentally sensitive
luminescent colorant exhibits a first excitation wavelength
.lamda..sub.exc and said luminescent standard exhibits a second
excitation wavelength .lamda..sub.exs, and said environmentally
sensitive luminescent colorant exhibits a first emission wavelength
.lamda..sub.emc and said luminescent standard exhibits a second
wavelength .lamda..sub.ems which are different.
18. A method of identifying changes in an ingredient within a core
material in a microcapsule according to claim 1, due to
environmental exposure comprising: (i) providing microcapsules
including a core material and an ingredient whose environmental
sensitivity is to be monitored, said microcapsule containing an
environmentally sensitive luminescent colorant exhibiting a first
set of luminescent characteristics and an environmentally
insensitive luminescent standard exhibiting a second set of
luminescent characteristics; (ii) measuring the first and second
set of luminescent characteristics of the microcapsules at a time
t.sub.0 and t.sub.1 in a given environment; (iii) examining the
difference between the first and second sets of luminescent
characteristics of said environmentally sensitive luminescent
colorant and said luminescent standard; (iv) identifying a change
in said ingredient associated with the difference in luminescent
characteristics identified in step (iii).
Description
FIELD OF THE INVENTION
The present disclosure relates to the incorporation of fluorescent
materials into microcapsules for monitoring oxidation.
BACKGROUND
Microcapsules may be used as a delivery device for a number of
substances. The microcapsules may act as a control release device,
allowing for release of a given substance at a desired rate by, for
example, degradation of the shell, or upon mechanical impact or
application of pressure. The microcapsules may also act as a
mechanism to protect certain substances sensitive to, for example,
oxygen, moisture, etc. However, some amount of oxygen or moisture
migration into the microcapsules may occur, which may lead to
chemical changes in the core material.
A method of determining such chemical variation due to, for
example, oxidation or moisture, includes sampling the microcapsules
and analyzing the core ingredients by liquid or gas chromatography
assays. However, such assays may take a considerable amount of time
to run and portions of the sample must be destroyed. Accordingly,
methods of analyzing chemical changes within the microcapsules that
are relatively non-invasive and/or less time intensive may be
useful.
SUMMARY OF THE INVENTION
An aspect of the present disclosure relates to microcapsules
comprising a shell material and a core material. The core material
may include an environmentally sensitive luminescent colorant which
exhibits characteristics of an emitted wavelength bandwidth, a peak
intensity for emission and a time for luminescence decay, one or
more of the characteristics capable of changing upon exposure to a
given environment and a luminescent standard which exhibits
characteristics of an emitted wavelength bandwidth, a peak
intensity for emission and a time for luminescence decay, one or
more of the characteristics not changing upon exposure to said
given environment.
A further aspect of the present disclosure relates to method of
forming microcapsules. The method may include mixing an
environmentally sensitive luminescent colorant and a luminescent
standard to form a core material and encapsulating the core
material in a shell material forming microcapsules. The
environmentally sensitive luminescent colorant may exhibit
characteristics of an emitted wavelength bandwidth, a peak
intensity for emission and a time for luminescence decay, wherein
one or more of the characteristics capable of changing upon
exposure to a given environment. The luminescent standard may
exhibit characteristics of an emitted wavelength bandwidth, a peak
intensity for emission and a time for luminescence decay, wherein
one or more of the characteristics do not change upon exposure to
said given environment.
Another aspect of the present disclosure relates to a method of
identifying changes in a core material and/or ingredient within
said core material in a microcapsule, due to environmental
exposure. The method may include: (i) providing microcapsules
including a core material, optionally containing an ingredient,
where the core material and/or ingredient's environmental
sensitivity is to be monitored, wherein the microcapsule may
contain an environmentally sensitive luminescent colorant
exhibiting a first set of luminescent characteristics and an
environmentally insensitive luminescent standard exhibiting a
second set of luminescent characteristics. The method may also
include (ii) measuring the first and second set of luminescent
characteristics of the microcapsules at a time t.sub.0 and t.sub.1
in a given environment; (iii) examining the difference between the
first and second sets of luminescent characteristics of the
environmentally sensitive luminescent colorant and the luminescent
standard; and (iv) identifying a change in the core material and/or
ingredient associated with the difference in luminescent
characteristics identified in step (iii).
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features of this disclosure, and the
manner of attaining them, will become more apparent and better
understood by reference to the following description of embodiments
described herein taken in conjunction with the accompanying
drawings, wherein:
FIGS. 1a and 1b illustrates cross-sections of examples of
microcapsules;
FIG. 2a illustrates an example excitation and emission spectrums
for a luminescent material;
FIG. 2b illustrates an example of decay of luminescent intensity
over a period of time;
FIG. 3 illustrates the emission spectrum of an example of an oxygen
sensitive luminescent colorant
(tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (II)
bis(hexafluorophosphate) complex) "A" in canola oil excited at 485
nm;
FIG. 4 illustrates the emission spectrum of an example of the
oxygen sensitive luminescent colorant illustrated in FIG. 3, an
emission spectrum of a luminescent standard and an emission
spectrum of a mixture of both the oxygen sensitive luminescent
colorant and the luminescent standard;
FIG. 5 illustrates the ratio of luminescent intensity over a period
of time between the oxygen sensitive luminescent colorant and the
luminescent standard in noncrosslinked microcapsules;
FIG. 6 illustrates the ratio of luminescent intensity over a period
of time between the oxygen sensitive luminescent colorant and the
luminescent standard in transglutaminase crosslinked
microcapsules;
FIG. 7 illustrates the ratio of luminescent intensity over a period
of time between the oxygen sensitive luminescent colorant and the
luminescent standard in clay soaked microcapsules;
FIG. 8 illustrates the ratio of luminescent intensity over a period
of time between the oxygen sensitive luminescent colorant and the
luminescent standard in microcapsules including layer by layer
formation;
FIG. 9 illustrates the ratio of luminescent intensity over a period
of time between the oxygen sensitive luminescent colorant and the
luminescent standard in clay soaked microcapsules including layer
by layer formation;
FIG. 10 illustrates the ratio of luminescent intensity over a
period of time between the oxygen sensitive luminescent colorant
and the luminescent standard in a variety of dried microcapsule
samples;
FIG. 11 illustrates the ratio of luminescent intensity over a
period of time between the oxygen sensitive luminescent colorant
and the luminescent standard in a variety of dried microcapsule
samples; and
FIG. 12 illustrates the ratio of luminescent intensity over a
period of time between oxygen sensitive luminescent colorant and
the luminescent standard encapsulated in micelles measured over a
period of time.
DETAILED DESCRIPTION
The present disclosure relates to a system and method for
monitoring oxidation or other chemical changes of core materials
encapsulated by microcapsules via fluorescence or, more generally,
luminescence. The microcapsules may incorporate an oxygen-sensitive
dye core material that may alter in its fluorescent intensity upon
exposure to oxygen, due to oxidation. Fluorescent spectroscopy, or
other measurement techniques, may then be used to indicate or
determine the degree of oxidation of the core materials within the
microcapsules. Oxidation herein may be understood as the loss of
electrons or hydrogen, and/or the gain of oxygen, and/or the
increase in the oxidation state, of the core material.
Microcapsules may generally be understood as small spheres or
particles that include a core material contained or dispersed in a
shell or matrix. FIG. 1a illustrates an example of the
cross-section of a microcapsule 10 including a core material 12
contained within a shell material 14. FIG. 1b illustrates an
example of a cross-section of a microcapsule 10 wherein the core
material 12 is dispersed throughout the shell matrix 14, which
forms a matrix around the domains of core material (also referred
to herein as a shell).
It may be appreciated that the core material may be dispersed
relatively uniformly through the microcapsule, providing a
relatively uniform percent volume throughout selected portions of
the microcapsules, or the core material may be dispersed relatively
randomly, wherein the core material may vary by percent volume
between 1 and 100 percent throughout selected portions of the
microcapsules. In addition, the microcapsules need not be
completely spherical in shape, i.e., maintaining the same radius
about a central point, but may exhibit a number of shapes,
including ellipsoid, as well as various irregular shapes.
The core material may include any material that may be
advantageously provided in a microcapsule. For example the core
material may include a carrier in which ingredients may be
provided. The carrier may include a solvent, such as a relatively
short chain hydrocarbon, such as a vegetable oil or mineral oil.
The ingredients may include, for example, pharmaceuticals,
flavorants, attractants (such as perfumes), colorants, etc.
Pharmaceuticals may be understood as herbs, vitamins, or other
natural or synthetic chemical substances utilized in the treatment,
prevention, cure or diagnosis of disease or to enhance physical or
mental well being. Examples of pharmaceuticals may include lutein
and retinol.
As alluded to above, the present disclosure contemplates
incorporating an oxygen sensitive luminescent dye or pigment
(referred to herein after as colorant) to provide an indicator of
oxidation of the core material and/or ingredient within the core
material. Luminescence may be understood as the absorption of a
portion of incident electromagnetic radiation at a first wavelength
or spectrum and the emission of electromagnetic radiation at a
second wavelength or spectrum. FIG. 2a illustrates an example of a
given excitation wavelength spectrum of a luminescent material and
a given emission wavelength spectrum of the luminescent material.
Each spectrum may exhibit peak wavelengths, (P.sub.excitation,
P.sub.emission), and band widths, (B.sub.excitaton,
B.sub.emission), which may vary in size depending on the
luminescent material and/or chemical and/or physical changes to a
given luminescent material. Band width may be defined by the range
of wavelengths employed for excitation or the range of wavelengths
observed during emission. Furthermore, the emitted radiation may
exhibit a peak intensity and a decay time, as illustrated in FIG.
2b, which may also vary depending on the luminescent material and
any chemical and/or physical changes to the luminescent
material.
As the colorant is exposed to oxygen and undergoes oxidation, the
luminescent properties or characteristics of the colorant may be
altered. For example, the span of the emitted wavelength bandwidth
may change or shift in the range of +/-50 nm. Accordingly, the
emitted wavelength may change or shift between +/-5 nm to 100 nm,
including all values and increments therein, in 0.1 nm increments.
In addition, the wavelength observed for the peak intensity for
emission may similarly shift in the range of +/-50 nm, such as a
shift between +/-5 nm to 50 nm, including all values and increments
therein, in 0.1 nm increments. Finally, as the colorant oxidizes,
the time for decay may change +/-0.5 to 5 seconds.
By contrast, the luminescent standard described herein may not be
subject to such changes upon exposure to a given environmental
condition (such as oxygen) individually or collectively. That is,
the span of the emitted wavelength bandwidth for the standard may
only change or shift in the range of less than +/-5 nm. Similarly,
the wavelength observed for peak intensity for emission may only
change in the range of +/-5 nm. Finally, the time for decay of the
luminescent standard may only change +/-0.01 to less than 0.5
seconds.
The luminescent colorant may be selected based upon a number of
factors, such as to avoid chemical interactions with the core
material, shell material and/or the colorant, the food and safety
requirements of the microcapsules, etc. In addition, the
luminescent colorant may be chosen based on the solubility of the
luminescent colorant in the core material. Where the core material
may be an oil based material, the luminescent colorant may be
chosen such that it may be soluble in the oil based material to
improve the distribution of the colorant in the formed
microcapsule. For example, the core material carrier and the
luminescent colorant may be chosen such that they have Hildebrand
solubility parameter values (.delta.) that are within +/-2.0 units
of one another, as measured in (MPa).sup.1/2. Those skilled in the
art may appreciate that the Hildebrand solubility parameter
represents the square root of the cohesive energy density and
provides a numerical estimate of the degree of interaction of
selected materials.
Furthermore, the luminescent colorant may be selected based upon
the rate the colorant oxidizes. As may be appreciated, the rate of
oxidation of the luminescent colorant and its changes in
luminescence may be different than the rate of oxidation and change
in luminescence of the oxygen sensitive core material. In such a
case, one may identify a correlation. As may be appreciated, the
oxidation rate of the luminescent colorant may be calibrated or
otherwise compared to the oxidation rate of the other materials
(e.g. ingredients) present in the microcapsule core material. Such
comparison may be developed either prior to encapsulation or
post-encapsulation by various testing mechanisms.
In one example the luminescent colorant may be an oxygen sensitive
fluorescent dye. Fluorescent may be understood as a form of
luminescence wherein molecular absorption of a photon, i.e.,
electromagnetic radiation, may trigger the emission of another
photon with a different wavelength, such as a longer wavelength.
Fluorescence may occur relatively quickly, such as in the range of
0.01 nanoseconds (ns) to a few seconds, including all values and
increments therein, such as in the range of 0.01 (ns) to 10
seconds. The luminescent colorant may include, for example,
ruthenium diimine complexes. In one example the luminescent
colorant may also include
tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (II)
bis(hexafluorophosphate) complex. The luminescent colorant may be
present in the core material in the range of 1000 ppm or less,
including all values and increments therein in 1 ppm increments,
such as in the range of 1 ppm to 50 ppm.
In addition to the luminescent colorant, a luminescent standard may
be utilized that may be relatively unaffected by oxidation, i.e.,
the standard may not be subject to oxidation. The standard may
retain its luminescent properties regardless of the amount or rate
of oxygen migration into the microcapsule. As may be appreciated
the standard may be utilized to calibrate the measurement device
with reference to changes that may occur, not only in the device
itself, but also in the shell or core materials of the
microcapsules as well as any slurry in which the microcapsules that
may cause variation in the measurements. In addition to
insensitivity to oxygen, in some examples, the luminescent standard
may also be insensitive to changes in pH.
The luminescent standard may also be chosen on the basis of its
solubility with other core materials. For example, the luminescent
standard may be chosen such that the core material and/or the
luminescent colorant have Hildebrand solubility parameter values
(.delta.) that are within +/-2.0 units of one another, as measured
in (MPa).sup.1/2. Those skilled in the art may appreciate that the
Hildebrand solubility parameter represents the square root of the
cohesive energy density and provides a numerical estimate of the
degree of interaction of selected materials.
Furthermore, it may be appreciated that luminescent standard may be
chosen based on luminescent interactions with the oxygen sensitive
luminescent colorant and/or core materials. For example, the
luminescent standard may exhibit at least one excitation wavelength
.lamda..sub.exs that may be relatively the same or different as at
least one excitation wavelength of the luminescent colorant
.lamda..sub.exc. The luminescent standard may exhibit at least one
emission wavelength .lamda..sub.ems that is different from that of
the luminescent colorant .lamda..sub.emc. Where other core
materials may exhibit luminescent characteristics, the excitation
wavelengths exhibited by the chosen luminescent standard and the
chosen luminescent colorant may be different from excitation
wavelength(s) exhibited by other core materials
.lamda..sub.exm.
For example, FIG. 3 illustrates the emission spectrum of an example
of an oxygen sensitive luminescent colorant
(tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (II)
bis(hexafluorophosphate) complex) "A" in canola oil excited at 485
nm. FIG. 4 illustrates the emission spectrum of the oxygen
sensitive luminescent colorant
(tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (II)
bis(hexafluorophosphate) complex) "A", an example of a luminescent
standard (DC108GY available from Angstrom Technologies) "B" and a
combination of the luminescent standard with the oxygen sensitive
luminescent colorant in canola oil excited at 485 nm "C". As can be
seen, the combination of the oxygen sensitive luminescent colorant
with the luminescent standard (curve "C") exhibited similar peak
intensities of the individual oxygen sensitive luminescent colorant
"P.sub.1" and the luminescent standard "P.sub.2." It may be
observed that the combination may exhibit relatively slight shifts
in the peak intensities and/or a shift in the wavelength where peak
intensity is observed.
In addition, the luminescent standard may be present in the range
of 50 ppm or less, including all values and increments therein,
such as in the range of 1 ppm to 50 ppm. Examples of luminescent
standards may include sulfonated coumarin dyes, sulfonated
rhodamine dyes, sulfonated xanthene dye, sulfonated cyanine dyes,
quantum dots, fluorescein, fluorescein derivatives, and/or
combinations thereof.
Microcapsules including core materials with the luminescent
colorant and the luminescent standard may be formed utilizing a
number of techniques, such as coacervation, centrifugal extrusion,
fluidized bed, spray drying, interfacial polymerization, reverse
phase interfacial polymerization, etc. Once formed the capsules may
be treated with a post-treatment process. The treatments may alter
oxygen permeability or improve mechanical stability.
For example, the microcapsules may be formed by complex
coacervation, which may be understood as when two or more
oppositely-charged macromolecular colloids are used to form an
aqueous solution, which may then be separated into two liquid
phases. The first phase, called the coacervate, may include the
colloid droplets, and the other liquid phase, called the
equilibrium liquid, may include an aqueous solution of the
coacervating agent. The core material may include oil based media,
such as various organic oils, e.g., vegetable oils, or mineral oils
and may be dispersed into a number of droplets through the
solution.
Coacervation of the colloids around oil based core materials
dispersed within the equilibrium liquid may occur at temperatures
greater than the gelation temperature T.sub.gel of the colloid
materials and may be triggered by, for example, a change in
temperature, addition of an acid, or addition of water. The
gelation temperature may be understood as the temperature above
which a gel will not form or, in other words, the temperature at or
below which the viscosity of the colloids may increase and form a
substantially infinite polymer network. It may be appreciated that
the gelation temperature may be affected by the concentration of
the colloid, the solvent, and other factors. The mixture may be
allowed to cool, allowing for a gel to form around the core
material, creating microcapsules. The microcapsules may be
post-treated by a number of processes including cross-linking, clay
soaking and layer-by-layer (LBL) formation.
In one example, a first colloidal precursor, such as gelatin
(mammalian or non-mammalian) or agar, may be added to a first
solvent, such as water, forming a solution. The first colloidal
precursor may be present in the solvent in the range of 0.1 to 5.0%
by weight of the precursor to the first solvent/precursor mixture,
including all values and increments therein. The solution may be
maintained at a temperature that is higher than the gelation
temperature T.sub.gel of the first colloidal precursor, such as
greater than 50.degree. C., including all values and increments in
the range of 50.degree. C. to 200.degree. C. However, it may be
appreciated that the temperature may be altered or varied,
depending on the colloids or core materials utilized.
The core material may then be added to the solution and dispersed
into the solution, forming a number of droplets or domains in the
solution. The domains may have an average diameter (or largest
linear dimension) of less than 100 .mu.m, including all values and
increments in the range of 0.1 .mu.m to less than 100 .mu.m. In
addition, the core material may be present at a ratio in the range
of 3:1 to 5:1 core material to first colloidal precursor by weight,
including all values and increments therein.
A second colloidal precursor may then be added, such as
carboxymethylcellulose, gum arabic or sodium hexametaphosphate. It
may be appreciated that the second colloidal precursor may exhibit
an opposite charge than the first colloidal precursor. The second
colloidal precursor may be present in the range of 10 to 30% by
weight of the combination of the first and second colloidal
precursors, including all values and increments therein. The second
colloidal precursor may be added in a second solution, wherein the
solution may include in the range of 1 to 10% of the second
colloidal precursor.
The pH may then be altered, such as by the addition of an
appropriate acid or base. In one example, the pH may be lowered or
adjusted in the range of 4.5 to 5.0 pH. The reaction mixture may
then begin to cool and gels may begin to form. Once cooled to room
temperature, the capsules may then be subjected to a post-treatment
process. The capsules may then settle and separated from the
supernatant and washed. It may be appreciated that the processes
may occur under an inert atmosphere, which may prevent the
oxidation of the core material. Exemplary inert atmospheres may
include N.sub.2 or Ar gas.
Examples of post treatment processes may include additional
cross-linking, clay soaking, and layer by layer (LBL) formation
utilizing various polycations and/or polyanions. It may be
appreciated that more than one post treatment processes may be
utilized as well. For example, the microcapsules may be treated
with additional crosslinking and then LBL formation.
For example, additional cross-linking with crosslinking agents may
be facilitated by mixing the microcapsules in a solution including
a crosslinking agent. The solution may include 5 to 50% of the
crosslinking agent, including all values and increments therein.
The microcapsules may be crosslinked for 1 minute to 20 hours,
including all values and increments therein, such as in the range
of 2 hours to 20 hours, 4 hours to 12 hours, etc. In some examples,
gelatin capsules may be crosslinked with gluteraldehyde or
transglutaminase.
In clay soaking, the microcapsules may be soaked in a solution of
exfoliated clay. Such clays may include kaolinite, betonite,
smectite, illite or chlorite clays. The microcapsules may be soaked
for a few minutes to 20 hours, including all values and increments
therein, such as 2 hours to 15 hours, 12 hours, etc. Clay soaking
may be utilized alone or in combination with both crosslinking and
LBL formation. In some examples, clay soaking may be performed
before other post-treatment processes and in other examples, it may
be performed after other post-treatment processes.
In layer by layer formation (LBL), layers of polycations,
polyanions or combinations thereof may be formed on the
microcapsules surface. Polycations may include, for example,
chitosan and polyanions may include, for example, clay or alginate.
Once microcapsule formation is completed, excess liquid may be
removed from the microcapsules such as through centrifuging and
decanting of the supernatant The LBL process may include dispersing
the microcapsules into pH 7 buffer and removing the microcapsules
from the buffer, such as by centrifuging and decanting. The
microcapsules may then be dispersed in a buffer having a pH of less
than 7, such as, for example 4, which may include either
polycations or polyanions, allowed to soak for a given period of
time and then removed from the buffer. The microcapsules may again
be dispersed into pH 7 buffer and again the capsules may be removed
from the buffer, such as by centrifuging and/or decanting. To
provide an additional layer, the microcapsules may be dispersed in
a buffer having a pH of less than 7, such as, for example 4, which
may include either polycations or polyanions, allowed to soak and
then may be removed from the buffer. The method may be repeated a
number of times while, for example, alternating the ionic layers.
Similarly, LBL formation may be performed in combination with the
other post-treatment processes, such as after crosslinking but
before clay soaking; after crosslinking and clay soaking, etc.
Once the microcapsules are formed, they may be provided in solution
or in dry form. To determine the oxidation of the core materials,
the luminescence of the microcapsules may be monitored and
determined periodically (at times t.sub.0 and t.sub.1) and a ratio
of the luminescent standard to the oxygen sensitive luminescent
colorant may be examined and compared to previous measurements. In
one example, the luminescence may be measured by a spectrometer. A
ratio between the luminescent standard and the oxygen sensitive
luminescent colorant may be determined and the degree of oxidation
may be gauged.
It may also be appreciated that the above may pertain, not only to
oxygen sensitive ingredients and luminescent colorants but also to
ingredients and corresponding luminescent colorants that may be
sensitive to other environmental components. Such environmentally
sensitive ingredients and luminescent colorants may include those
that may exhibit chemical or physical changes upon exposure to one
or more of moisture, a particular gas (such as oxygen, carbon
dioxide, carbon monoxide etc.), a particular solvent (such as
aqueous solvents, hydrocarbon based solvents, etc.), variations in
pH and/or other particular substances that may adversely affect the
activity of an ingredient contained within a microcapsule. An
example of water sensitive luminescent colorants includes, but is
not limited to,
N,N'-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)ethyle-
nediamine (IANBD amide), and an example of pH sensitive luminescent
colorants includes, but is not limited to, SNARF-4F 5-(and
-6)-carboxylic acid, both available from Invitrogen. The
environmentally sensitive luminescent colorant may, therefore, be
chosen on the basis described above and used in combination with an
appropriately selected luminescent standard as described above. For
example, the luminescent colorant may be chosen on the basis that
an ingredient is sensitive to a given environment, i.e., a
particular substance which the microcapsules may be exposed. The
luminescent standard may be chosen based on its relative lack of
sensitivity to such environment.
EXAMPLES
The following examples are presented for illustrative purposes only
and therefore are not meant to limit the scope of the disclosure
and claimed subject matter attached herein.
Various microcapsule formulations were provided using complex
coacervation, in-situ polymerization and the formation of micelles.
The oxygen stability (i.e., as indicated by the oxidation of the
oxygen sensitive luminescent colorant) of the various microcapsule
formulations was tested both in aqueous slurries and as dry paste
by measuring the luminescence (i.e., luminescent signals) of the
microcapsules over a given period off time by spectrophotometer
analysis.
Core Material
The standard core material was produced by combining canola oil
with up to 20 ppm of oxygen sensitive fluorescent dye, a
tris(4,7-diphenyl-1,10-phenathroline)ruthenium (II)
bis(hexafluorophosphate) complex, and up to 20 ppm of an inert
luminescent standard.
Microcapsules Formed by Complex Coacervation
A number of microcapsules were formed by complex coacervation by
dissolving 10 grams of 300 Bloom Type A gelatin in 400 mL of
deionized water at 60.degree. C. Then, 40 grams of core material
was homogenized into the gelatin solution to form droplets less
than 100 .mu.m in diameter. 20 mL of 5% sodium hexametaphosphate
solution was added to the gelatin solution. The pH of the solution
was then lowered to approximately 4.8 upon the addition of 10%
acetic acid. The reaction mixture was then allowed to cool to room
temperature, followed by post-treatment (described below). The
capsules were then allowed to settle, were separated from the
supernatant and washed three times with fresh deionized water. All
steps were carried out under an inert gas N.sub.2 or Ar.sub.2 to
prevent oxidation. Fish gelatin microcapsules were also
produced.
Microcapsules Formed by In-Situ Polymerization
Microcapsules including a urea-formaldehyde shell were prepared by
mixing 50 mL of a 10% ethylene maleic anhydride solution with 2.5
grams of urea and 0.25 grams of resorcinol at room temperature.
Approximately 30 mL of ultra pure water was added to the mixture.
The pH of the mixture was then raised to 3.7 with a concentrated
solution of NaOH. 25 g of core material was emulsified into the
aqueous solution and then 6.7 g of formaldehyde was added. The
system was heated to 60.degree. C. for at least 2 hours. The
microcapsules were isolated for testing once the solution cooled.
The solutions were purged and reacted under inert conditions during
processing to prevent oxidation.
Post Treatment
After the various microcapsules were produced, a number of
post-treatment processes were performed using three methods of
post-treatment alone or in combination. The first method included
cross-linking the microcapsules produced by complex coacervation.
Two cross-linking agents, gluteraldehyde and transglutaminase, were
separately utilized. A first 50 gram batch of gelatin microcapsules
were crosslinked with 5 mL of a 25% gluteraldehyde solution over a
time period of 4 (for glut-lite samples) to 12 hours for the
remainder of the samples crosslinked with gluteraldehyde. A second
batch was cross-linked by soaking microcapsules in 0.1% (w.t.)
transglutaminase overnight.
A second method of post-treatment included depositing clay onto the
surface of the microcapsules. The microcapsules were soaked in a
solution of exfoliated clay for 12 hours either before or after
other post treatment processes.
The third method of post treatment included layer by layer
development on the surface of the microcapsules. First a dispersion
of microcapsules were centrifuged and the supernatant was decanted.
The microcapsules were then redispersed into a pH 7 buffer. Then
the capsules were centrifuged and the supernatant was decanted. The
capsules were then redispersed into a buffer of 4 pH containing
alginate or clay. The capsules were centrifuged and decanted again,
redispersed in a 7 pH buffer and again centrifuged and decanted.
The capsules were then redispersed in a pH 4 buffer including
chitosan and centrifuged and decanted. Dispersal of the capsules in
a 7 pH buffer was again alternated by dispersal into a 4 pH buffer
including either the polyanion or polycation followed by
centrifuging and decanting until two additional layers of the
polyanion and polycation were formed over the microcapsule.
Table 1 below summarizes the microcapsule formulations and
post-treatments. The various order in which post-treatment occurred
where more than one post-treatment process was applied is also
described in the table below for each sample.
TABLE-US-00001 TABLE 1 Sample Formulations Sample Number Shell
Cross-linking Shell Treatment 1 300 Bloom Type A Gelatin None None
2 300 Bloom Type A Gelatin Gluteraldehyde None 3 300 Bloom Type A
Gelatin Transglutaminase None 4 Urea-Formaldehyde None None 5 Fish
Gelatin Transglutaminase None 6 300 Bloom Type A Gelatin None
Microcapsules were soaked in a solution of exfoliated kaolin clay 7
300 Bloom Type A Gelatin None Microcapsules were soaked in a
solution of exfoliated sodium bentonite clay 8 300 Bloom Type A
Gelatin Transglutaminase Microcapsules were soaked in a solution of
exfoliated kaolin clay before crosslinking 9 300 Bloom Type A
Gelatin Transglutaminase Microcapsules were soaked in a solution of
exfoliated sodium bentonite clay before crosslinking 10 300 Bloom
Type A Gelatin Transglutaminase LBL formation was used to deposit a
layer of clay and a layer of chitosan after crosslinking 11 300
Bloom Type A Gelatin Transglutaminase LBL formation was used to
deposit two layers of clay and a layer of chitosan in between after
crosslinking 12 300 Bloom Type A Gelatin None LBL formation was
used to deposit 5 layers of alternating bentonite clay and chitosan
13 300 Bloom Type A Gelatin None LBL formation was used to deposit
5 layers of alternating bentonite clay and chitosan, with
additional soak time between the layers 14 300 Bloom Type A Gelatin
None LBL formation was used to deposit ten alternating layers of
clay and chitosan 15 300 Bloom Type A Gelatin Transglutaminase LBL
formation was used to deposit five alternating layers of clay and
chitosan after crosslinking 16 300 Bloom Type A Gelatin
Transglutaminase LBL formation was used to deposit five alternating
layers of clay and chitosan with additional soak time in between
the layers after crosslinking 17 300 Bloom Type A Gelatin
Transglutaminase LBL formation was used to deposit ten alternating
layers of clay and chitosan after crosslinking 18 300 Bloom Type A
Gelatin Transglutaminase First the microcapsules were soaked in
bentonite and then LBL formation was used to deposit ten
alternating layers of clay and chitosan before crosslinking 19 300
Bloom Type A Gelatin Transglutaminase First the microcapsules were
soaked in kaolin and then LBL formation was used to deposit ten
alternating layers of clay and chitosan before crosslinking
Oxygen Barrier Analysis
Stability experiments were carried out on microcapsule aqueous
slurries, wherein the microcapsules were prepared as described in
the samples above. In the following stability analysis, six batches
of microcapsule slurries were formed by dispersing approximately 4
grams of microcapsules in 40 mL of water.
A first stability tests were performed on the microcapsules
prepared as described in example 1, which were then, as described
above, dispersed in water. A first set (three batches) of
microcapsule slurries were maintained under an inert atmosphere
(N.sub.2 or Ar) through the stability testing and labeled the
control. Another set (three batches) of microcapsule slurries were
agitated at room temperature and exposed to air. The air exposed
capsules were placed in a beaker with a magnetic stir bar to
continuously agitate the solution. Periodically, 0.2 mL of
microcapsules was collected from each set of samples and the
fluorescence of the samples was measured.
The fluorescence spectra of the core materials were collected with
a Perkin Elmer LS50B Luminescence Spectrometer. Fluorescence of the
microcapsule samples was monitored with a Beckman Coulter DTX880
Multimode Detector. Microcapsule samples were excited at 485 nm and
measurements were made at 535 nm and 625 nm. A ratio of the
luminescent standard signals and the oxidation sensitive
luminescent colorant signals were used to quantify core material
oxidation.
As illustrated in FIG. 5, the three batches (labeled as Trials 1-3
O2) exposed to air exhibited a 90% drop in luminescent signal over
200 hours, indicating oxidation of the core materials. The purged
samples (those maintained under an inert atmosphere) (labeled as
Trials 1-3 N2) remained relatively stable over the 200 hour time
period. Optical micrographs of the microcapsules before and after
the study revealed that the capsules agitated under air fell apart
and were not present at the end of the 200 hour period. Thus, the
detected luminescent signal for the microcapsules agitated in air
did not reflect the oxygen barrier properties of the gelatin; as
the capsules fell part, the core material was exposed to the
surrounding environment resulting in relatively rapid oxidation.
Without being bound to a particular theory, it appears the
agitation of the air exposed capsules using the stir bar caused
rupture of the capsules via shear forces. Accordingly, testing of
the capsules exposed to air was modified to agitate in a shaker to
avoid the introduction of shear forces. However, these capsules
fell apart as well.
Crosslinking methods, such as in samples 2 and 3, were utilized to
prevent the breakdown of the capsules. Gluteraldehyde was
investigated as a crosslinking agent (sample 2) in stability
studies, as outlined above (i.e., 4 grams of microcapsules were
mixed with 40 mL of water and batches were agitated in both inert
and air atmospheres maintained at 25.degree. C.) and the
luminescence was measured over a course of 200 hours. However,
relatively low luminescent intensity was exhibited and relatively
little signal change was observed through the course of the trial.
Without being bound to a particular theory, it appears that
cross-linking with gluteraldehyde caused some degree of change in
microcapsule color, which blocked at least a portion of the
excitation and/or emission light. Transglutaminase was then
utilized as a crosslinking agent (sample 3). Microcapsules from
sample 1 were crosslinked overnight with 0.1% transglutaminase
(with respect to gelatin weight). A portion of the crosslinked
microcapsules were agitated in air and another portion of the
crosslinked microcapsules were agitated in an inert environment.
FIG. 6 illustrates the results of the stability analysis, which
occurred at a temperature of 25.degree. C. over a period of
approximately 325 hours. The ratio of the oxygen sensitive
luminescent colorant to the luminescent standard remained
relatively constant for both samples for up to approximately 72
hours. However, after this initial time period, the measured
luminescence for the samples exposed to air dropped in a relatively
rapid manner. The relatively rapid drop appears to have
corresponded with a mechanical breakdown of the microcapsules. It
is noted that the samples maintained in the inert atmosphere did
not exhibit a similar deterioration and breakdown.
Clay soaked microcapsules, crosslinked with transglutaminase, were
then tested, such those illustrated in samples 8 and 9. After
forming the microcapsules as in sample 1, the microcapsules were
soaked in either kaolin or bentonite clay and then crosslinked.
Oxygen stability tests were performed on each sample set in both
inert and air exposed atmospheres and the luminescence of the
microcapsules were measured at various intervals. The results of
the testing is illustrated in FIG. 7, which demonstrates that the
purged samples exhibit a higher luminescent ratio and a slow decay
in the ratio, whereas the air exposed samples illustrated a
relatively sharp decline in luminescent ratio and appeared to be
saturated with oxygen within three days. Optical microscopy of the
capsules indicated that the capsules fell apart.
Microcapsules were then provided that were crosslinked and provided
with ionic layers of clay and chitosan through LBL formation after
crosslinking as described in samples 10, 11, 15, 16 and 17. Various
layer configurations were examined, including 2 layers, 3 layers, 5
layers and 10 layers (samples 10, 11, 15, and 17, respectively). In
addition, a 5 layer configuration, wherein the layers were formed
using additional soak time (sample 16) was examined. Each
configuration was tested in both inert and air exposed atmospheres
and the luminescence was measured periodically. FIG. 8 illustrates
that the purged/inert samples exhibited relatively higher
fluorescent ratios with some decay in intensity over time. With
respect to the samples exposed to air, the two layer and three
layer samples fell apart after approximately two days and exhibited
a sharp decay in intensity. The five to ten layer samples exhibited
a relatively less significant decrease in intensity and the
microcapsules remained intact over the course of testing. The 5
layered long soaked samples exhibited a relatively lower intensity
than the base 5 layer samples; however, the rate of decrease
appeared to be relatively similar to the base 5 layer samples. The
10 layer samples exhibited a relatively higher rate of oxidation
between 100 and 150 hours.
Another study was performed with microcapsules that included the
addition of five polyanionic or polycationic layers to
microcapsules by layer by layer formation that had already been
soaked in either kaolin or bentonite clay. Once again, the
microcapsules were tested for oxygen stability and the luminescence
was measured periodically over the course of testing. The results
of the stability testing are illustrated in FIG. 9. The
purged/inert microcapsules were relatively stable over the course
of testing, whereas the air exposed microcapsules exhibit a
decrease in intensity after approximately 2 days and at the end of
140 hours disintegrated, as confirmed by optical microscopy.
Dry Capsule Testing
Dry microcapsule samples of transglutaminase crosslinked
microcapsules (sample 3), microcapsules formed from fish gelatin
(sample 5), microcapsules formed from urea formaldehyde (sample 4),
2 LBL formation treated microcapsules (sample 10), 3 LBL treated
microcapsules (sample 11), microcapsules soaked in kaolin clay
(sample 6) and microcapsules soaked in bentonite (sample 7) were
prepared by centrifuging 50 ml of microcapsule slurry at 3200 rpm
for 10 minutes. The precipitate was placed into the wells of a 96
well plate. The plate and microcapsules were dried in a vacuum
overnight at 40.degree. C., followed by fluorescence kinetic
measurements, discussed further below. The microcapsules were
exposed to air and stored in the analyzer between luminescent
sampling. Each cell was analyzed in a 4.times.4 array to produce 16
measurements within the cell. The measurements were averaged and
FIG. 10 illustrates the averaged results. The slope of the line was
used to characterize the oxidation of the core material, under the
assumption was made that the oxygen diffusion rate into the
microcapsules was linear.
Furthermore, each sample (samples 1-17 in Table 1 above) prepared
in slurry was dried and oxygen stability tested as a dry powder.
Three samples of each composition were tested twice for 12 hours at
40.degree. C. resulting in 6 data sets for each composition. The
normalized averages of these sets are illustrated in FIG. 11, which
also illustrates the standard deviation. As can be seen in the
figure, the non-crosslinked samples (sample 1) offered relatively
better protection from oxygen than the remainder of the
formulations; however, the mechanical stability of this formulation
may be problematic (i.e. see FIG. 5). The gluteraldehyde
crosslinked samples (sample 2) offered what appeared to be
relatively good protection from oxygen as well.
In comparison, an alternate gelatin (fish gelatin crosslinked with
transglutaminase) and a non-gelatin sample (urea-formaldehyde)
(sample 4) were examined. The crosslinked fish gelatin exhibited a
relatively better barrier performance than the crosslinked
transglutaminase samples and the lightly crosslinked gluteraldehyde
samples. The poly(urea formaldehyde) exhibited relatively stable
fluorescence and yielded oxygen barrier performance analogous to
that of the fish gelatin.
The soaking of the microcapsules in the various clays (samples 6
and 7) demonstrated that the benefits may be somewhat negligible
over the use of other methods. However, the bentonite soaked
samples exhibited better oxygen stability over the kaolin clay
samples.
In addition, the sampling indicated that increasing the number of
layers applied by LBL formation improved the oxygen barrier
performance of the microcapsules, despite relatively large
deviations. It is noted that allowing the microcapsules to soak in
the ionic solution for longer time periods (sample 16) did not
necessarily result in better oxidation stability. In addition, the
2 layer sample, (sample 10) exhibited relatively poor oxygen
barrier performance. Without being bound to any particular theory,
it appears that the gelatin hydrates and swells, allowing for the
penetration of electrolytes into the gelatin shell. The penetration
and plasticization may decrease the oxygen barrier performance of
the gelatin.
The formulations that were soaked in clay, crosslinked with
transglutaminase and then provided with 5 alternating layers of
clay and chitosan by LBL formation exhibited relatively better
oxygen barrier performance that the 5 LBL microcapsules without
prior clay soaking. In addition, the bentonite soaked, crosslinked
and clay layered sample, exhibited relatively similar oxygen
barrier performance as the sample without bentonite soaking (sample
15).
Finally, relatively large performance enhancements were exhibited
by the 10 layer LBL formation sample (sample 17) and the
crosslinked, kaolin soaked, 5 layer LBL formation sample. However,
the relatively large degree of error is noted. In addition, it is
also noted that LBL formation may be relatively complex and
time-consuming.
Micelles
Micelles were then prepared using the same standard core material
described above. 80 grams of Tween 80 was placed in a closed system
purged with Ar and was stirred. 12 grams of the canola oil and
colorant mixture was slowly added to the Tween via syringe to form
a homogenous solution. Then 200 ml of ultra pure water was added
drop wise for approximately 1 hour while stirring. The solution was
stirred under Ar at room temperature for 72 hours. The average
diameter of the micelles were 255 nm.
The micelle solution was periodically tested (i.e., the
luminescence was measured) as a slurry over a 2 hour period to
generate data for calculation of an oxidation rate. FIG. 12
illustrates the results. It appears that the core material
oxidation was divided into two mechanisms as illustrated in FIG.
12, the first being free oil oxidation and the second being the
oxidation of encapsulated oil. As may be appreciated, and without
being bound to any particular theory, unlike in complex
coacervation or in-situ polymerization, micelles exhibit less than
100% encapsulation efficiency. Free unencapsulated oil was present
in the solution and oxidized at a much faster rate than the
encapsulated oil. Assuming linear oxidation, the normalized
oxidation rate was determined to be 5.2, which appears to be about
5 times greater than the gelatin microcapsules.
The foregoing description of several methods and embodiments has
been presented for purposes of illustration. It is not intended to
be exhaustive or to limit the claims to the precise steps and/or
forms disclosed, and obviously many modifications and variations
are possible in light of the above teaching. It is intended that
the scope of the invention be defined by the claims appended
hereto.
* * * * *
References